Natural progesterone is a hormone produced by both women and men, although to a lesser extent in men, and is an important precursor in the biosynthesis of other hormones in the human body. The use of natural progesterone has been linked to the relief of hot flashes, mood swings, bloating, loss of libido, vaginal dryness, and other uncomfortable symptoms associated with menopause and pre-menstrual syndrome (PMS). It is also useful in counteracting the damaging effects of estrogen dominance. Natural progesterone attaches to and blocks the receptors for estrogen molecules and estrogen-like compounds, causing them to travel through the body and eventually to be metabolized and excreted in urine. Natural progesterone also has been shown to alleviate, prevent, or even actually reverse osteoporosis.
Natural progesterone typically is taken orally as a capsule or tablet. While this form has the advantage of being very convenient, absorption of the progesterone via the digestive tract is very inefficient because 85-90% of the progesterone will be metabolized immediately by the liver and excreted in bile. When taken orally, the progesterone, like other fat-soluble nutrients, is taken up by the portal vein and transported directly to the liver where much of it is metabolized and conjugated for excretion. As a result, the amount of ingested progesterone required to be effective may be up to 10-25 times higher than if the progesterone is absorbed directly into the body via the skin. Large doses of oral progesterone may have negative side effects, including elevated levels of metabolites and unnecessary liver stress.
Topically applied progesterone creams or lotions do not contain as large an amount of progesterone because it may be absorbed directly by the body. The cream or lotion usually contains one or more transdermal carriers that carry the progesterone through the skin into the fatty tissues where the progesterone may be absorbed naturally into the bloodstream. The specific transdermal carrier is very important because some carriers (such as mineral oil) will cause the progesterone to decompose while on the surface of the skin, thus reducing or losing its effectiveness. Carriers that have slow transdermal penetration rates may require higher concentrations of progesterone to achieve sufficient progesterone absorption. In addition, most creams stay on the skin surface for a prolonged period of time, thus making use inconvenient. It is generally desirable to have a cream or lotion that is substantially absorbed by the skin very quickly, e.g., 30 seconds or less.